Cinders Posted June 10, 2021 Report Share Posted June 10, 2021 Hi all! I'm still at it with my .308, trying to figure out a weird split pattern I'm getting. Had to take a break during the Great Ammo Shortage of 'ought 20. Also just found out my Timney trigger is defective 😞 So working on replacing that. I'm getting a little fed up trying to find the problem with my rifle, it's a slow process of trying to borrow parts or to get to the range (or get ammo). Would a gunsmith be able to diagnose my rifle? It could be the barrel, the gas block, the compensator (swapped scope/mount out, roughly the same split pattern as before). Thanks! Quote Link to comment Share on other sites More sharing options...
jtallen83 Posted June 10, 2021 Report Share Posted June 10, 2021 Which Gunsmith? Gonna throw a link up here to your previous thread..... then I'll read it  Quote Link to comment Share on other sites More sharing options...
shooterrex Posted June 10, 2021 Report Share Posted June 10, 2021 Did you ever try another scope and mount? I also had a build showing erratic groups. Gas block was touching the rail . Quote Link to comment Share on other sites More sharing options...
Cinders Posted June 11, 2021 Author Report Share Posted June 11, 2021 Thanks for linking that! Yeah, I tried a better scope with a different mount and the grouping got a little worse but with the same pattern (2 tight groups left and right of the aim point). I did read your gas block reference, Rex, and I'm wondering if I can just run it by a real expert who can give me a more definite answer. It is a process to get to a range (and find ammo), so I'm not so keen on slowly trying out a scope swap, removing compensator, re-torque barrel, taking apart gas block to see if I can figure out if it was touching something.  Also, good question: which gunsmith? I'm asking is if this is even a thing to approach a gunsmith about.  Quote Link to comment Share on other sites More sharing options...
Belt Fed Posted June 11, 2021 Report Share Posted June 11, 2021 If something is off on your rifle a good gunsmith should be able to find it. You should be able to just look at your gas block inside the rail and see it it's touching. Quote Link to comment Share on other sites More sharing options...
shooterrex Posted June 11, 2021 Report Share Posted June 11, 2021 A gunsmith is going to have to do a lot of the same things you can do. Take the rail off. That will eliminate anything touching the gas block or barrel. Set the magazine on a sand bag and shoot it at 25 yds or so. Just change 1 thing at a time. A gunsmith is going to have to take it to the range and shoot it too. Quote Link to comment Share on other sites More sharing options...
DustBuster Posted June 11, 2021 Report Share Posted June 11, 2021 On 6/10/2021 at 4:28 PM, shooterrex said: Did you ever try another scope and mount? I also had a build showing erratic groups. Gas block was touching the rail . I also have been seeing bad groups... today they were split... I made some previous posts about my shooting and grouping... Asking everybody about rings, scopes, ammo and brass, as well as my gas block.  It is, as Shooter Rex’s once was, about a business card clearance from the inside of handgaurd.  I did notice slight markings inside the handgaurd before, but today after closer inspection, I’m sure it is rubbing when the barrel harmonically whips.  I am going to tear it off this weekend and look at the gas port, and either reinstall a non-adjustable one with more clearance or grind some material off.  I definetely also had at least one distinct split group today... Quote Link to comment Share on other sites More sharing options...
DustBuster Posted June 11, 2021 Report Share Posted June 11, 2021 Here is the most distinct split.  Reload ammo, same cases.  Pretty rock solid prone position.  I think it’s my gas block rubbing and it could be yours too, Cinders. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted June 12, 2021 Report Share Posted June 12, 2021 23 hours ago, Cinders said: Also, good question: which gunsmith? I'm asking is if this is even a thing to approach a gunsmith about.  The only gunsmith I'd trust to diagnose an AR would be ADCO Firearms. You'll have to call on the phone, and explain the situation - but there is no better commercial AR Gunsmith than ADCO. https://adcofirearms.com/ Quote Link to comment Share on other sites More sharing options...
Cinders Posted June 12, 2021 Author Report Share Posted June 12, 2021 Thanks, 98Z!  Yeah, Dust, that looks pretty similar. Mine are split a little more, but very tight groups in 2 distinct places, rather than a looser grouping. Quote Link to comment Share on other sites More sharing options...
Cliff R Posted June 13, 2021 Report Share Posted June 13, 2021 Have you taken the human factor out of the equation?.....FWIW......Cliff Quote Link to comment Share on other sites More sharing options...
Magwa Posted June 13, 2021 Report Share Posted June 13, 2021 1st question what ammo are you using that has to be the first look to then look for other issues but if it is garbage in it is garbage out... Quote Link to comment Share on other sites More sharing options...
mtrmn Posted June 13, 2021 Report Share Posted June 13, 2021 I have seen this discussed on other forums and it seemed to be narrowed down, in at least one case, to be dependent on which side of the magazine the round came from. If firing from a full mag, rounds 1,3,5 had about the same POI and rounds 2,4, had a different POI. This possibility could be eliminated by only loading one rd in the mag at a time so that every shot originated from the same side of the mag. If the split grouping went away then that would be the likely cause. I don't know if or how the problem ever got fixed however. Quote Link to comment Share on other sites More sharing options...
unforgiven Posted June 13, 2021 Report Share Posted June 13, 2021 You could strap down the rifle taking you out of the equation. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted June 14, 2021 Report Share Posted June 14, 2021 10 hours ago, mtrmn said: I have seen this discussed on other forums and it seemed to be narrowed down, in at least one case, to be dependent on which side of the magazine the round came from. If firing from a full mag, rounds 1,3,5 had about the same POI and rounds 2,4, had a different POI. This possibility could be eliminated by only loading one rd in the mag at a time so that every shot originated from the same side of the mag. If the split grouping went away then that would be the likely cause. I don't know if or how the problem ever got fixed however. That would definitely be because of the ejector...  Rounds feeding from the right side of the mag have to make that jump when chambering, because the ejector is on the left side of the bolt face. Square-faced ejectors are the worst offenders causing this, especially in the large-frame ARs. Quote Link to comment Share on other sites More sharing options...
mtrmn Posted June 14, 2021 Report Share Posted June 14, 2021 6 hours ago, 98Z5V said: That would definitely be because of the ejector...  Rounds feeding from the right side of the mag have to make that jump when chambering, because the ejector is on the left side of the bolt face. Square-faced ejectors are the worst offenders causing this, especially in the large-frame ARs. Simple enough. Now I understand more about the reasons behind the round ejectors. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted June 15, 2021 Report Share Posted June 15, 2021 15 hours ago, mtrmn said: Simple enough. Now I understand more about the reasons behind the round ejectors. Exactly so. Quote Link to comment Share on other sites More sharing options...
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